package com.test.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次
        resp.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);

        //得到图片
        Graphics2D graphics = (Graphics2D)image.getGraphics(); //画笔

        //设置图片的背景颜色
        graphics.setColor(Color.white);
        graphics.fillRect(0,0,80,20); //填充背景颜色

        //给图片写数据
        graphics.setColor(Color.BLUE); //画笔设置为蓝色
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求使用图片的方式打开
        resp.setContentType("image/jpeg");

        //网站存在缓存，不让浏览器缓存
        resp.setHeader("expires","-1");
        resp.setHeader("cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

    /**
     * 生成随机数
     * @return
     */
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer stringBuffer = new StringBuffer(); // 可变字符串
        // 填充0
        for(int i = 0; i < 7-num.length(); i++){
            stringBuffer.append(0);
        }
        String s = stringBuffer.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //
    }
}
